The present invention relates to steam turbines and, in particular, to monitoring eccentricity in the rotor of steam turbines.
The eccentricity of a rotor in a steam turbine is an indicator of the bowing of the rotor shaft and is generally indicative of the vibratory condition of the turbine during transient and steady state operations. The amount of eccentricity in a turbine rotor has a significant impact on the availability, reliability, performance and operational life of a turbine rotor.
Frequent steam turbine startups and shutdowns, which is common in combined steam turbine and gas turbine cycle units, tend to increase rotor eccentricity. An increase in eccentricity beyond a predetermined threshold limit indicates a permanent bow in the rotor. Excessive rotor bow typically results in rotor unbalance, which causes vibration of the rotor, and may lead to rubs between the rotating components and the stationary components of a steam turbine. Rubbing can degrade performance of a steam turbine and increase operating costs.
Current methods of monitoring eccentricity of a steam turbine involve displacement probe sensors mounted on the steam turbine and adjacent the rotor. The sensor data is stored in databases and manually downloaded to a computer for analysis. The probe sensor data is searched to select data associated with specific turbine events (e.g., shut-down, start-up and/or low speed rotor operation). Calculations are performed on the selected data manually to obtain baseline eccentricity values and eccentricity changes from startup to startup. This conventional method is less difficult when the turbine for which baseline eccentricity calculations are performed has relatively few start/stop cycles, but becomes tedious when the turbine has many such cycles. Performing manual calculations for a large volume of displacement sensor data is extremely time consuming and susceptible to error.